CHAPTER 3: KEY ITS DATA ELEMENTS FOR GOVERNMENT REPORTING SYSTEMS

3.1 GENERAL OBSERVATIONS ON ITS DATA SOURCES

During the matching exercise, several characteristics of existing ITS data sources relevant for government reporting systems became apparent. These characteristics are highlighted below.

3.1.1 All ITS Data Sources

Location referencing for ITS and traditional databases are extremely inconsistent. This is true between traditional databases as well. Resolution of location referencing issues is tantamount to coordinating any other data elements between the two realms. This involves not only the location of fixed highway features and events, but also the coordination of network definitions. For example, beginning and ending segments of HPMS segments must be related to the link/ node definitions used by the TMDD. Also, the location of ITS detectors relative to HPMS, TMG, and other traditional systems must be determined.

Definition of a "reportable crash," as required by traditional safety databases, is not covered in detail in the ITS data dictionaries. For example, "type of incident" for the TMDD and P1512 Data Dictionary includes whether a "crash" occurred, but no formal definition of a crash is given. Similarly, many ITS data element definitions and valid values are not fully explained. It does appear, however, that developers of the ITS data dictionaries are increasingly referencing standard transportation sources (e.g., the Highway Capacity Manual) in their updates.

Message sets are composed of data elements that are defined in each unique data dictionary plus data elements defined elsewhere. For example, the P1512 message sets use TMDD data elements. In some cases, the presence of a data element in an ITS source is not enough to link it directly with a traditional data system - the data relationship must be properly established. Examples include:

• FARS and Other Safety Databases/Person-Level Crash Severity - the TMDD has a data element on injuries but if this is related only to the entire crash and not persons, the safety database elements cannot be derived.
• Traffic volume - a collection time must be linked with traffic volume. For use with the TMG, the collection time must be one hour or less.

3.1.2 Traffic Management Data Dictionary

• Locational information is coded as x-y (lat/long) coordinates for network features and events. Traditional locational data items such as state, county, and urban area are not coded for features but theoretically could be derived from the coordinates.
• Incident response times by individual agency are generally not available (first responder only)
• Crash occupant information is not available
• Rural/urban distinctions are not made
• No allowance is made for the collection of vehicle classification data as a form of monitored traffic data.

3.1.3 National ITS Architecture

• Coding of vehicle type is inconsistent with traditional schemes and philosophies. The coding in the NA allows the following vehicle types:
  • tractor unit plus articulated trailer (van type)
  • tractor unit only
  • vehicle plus trailer, i.e. the motive power unit may carry payload (van type)
  • tractor unit plus articulated trailer plus trailer (van type)
  • tractor unit plus articulated trailer (tanker type)
  • vehicle plus trailer, i.e. the motive power unit may carry payload (tanker type)
  • tractor unit plus articulated trailer plus trailer (tanker type)
• Many of the data flows have been superceded by the ITS data dictionaries (e.g., current information on incidents). In these cases, the flows from the Architecture have not been repeated in the matching tables.
• The data flows and data elements usually do not have detailed formatting or valid values associated with them. Rather, they can be viewed as "set-asides" whereby more detailed standards (e.g., message sets and data dictionaries) define the information more precisely.
• Data for the National Transit Database is in short supply from all ITS sources. The Architecture does have several generic data flows, though, but how these are implemented is another question:
  • Transit_fare_transaction_records
  • Transit_incident_information
  • Transit_route_details
  • Transit_route_fare_data
  • Transit_route_operational_data (number of passengers by time of day)
  • Transit_vehicle_maintenance_log
  • Transit_vehicle_mileage_accumulated

3.1.4 P1512 Incident Management

• The details on vehicle configuration are given in P1512.3, Standard for Hazardous Material Incident Management Message Sets for Use by Emergency Management Centers. It is doubtful if any of these data will be available for crashes that do not involve hazardous materials.
• Matching incident data with TMDD is problematic - a common key or identification number, identifying a unique incident - is required.

3.1.5 Commercial Vehicle Information Exchange Window (CVIEW)

• Commercial Vehicle Information Exchange Window (CVIEW) contains tables that store information about commercial vehicles including vehicle registrations, permits, and violations records. This equipment package supports the exchange of safety and credentials data between agencies (for example, an administrative center and the roadside check facilities) within a single jurisdiction. Data are collected from multiple authoritative sources and packaged into snapshots (top-level summary and critical status information) and profiles (detailed and historical data). While some information is available concerning the number of reported accidents in a specific time period (i.e., last 15 months or last 2 years) from compliance reviews identified in the "Carrier Table", no details (such as time of day, occupants, whom was involved, cause, loss of hazardous materials) are available for individual events. The following are some characteristics of data elements available in CVIEW:
  • Vehicle identification data is available, such as VIN, license plates, and hazardous cargo permits
  • Specifics relating to vehicle characteristics are available, such as number of axles, make, model, year of manufacture, and gross vehicle weight
  • Does not include any information relating to roadways or weigh stations, such as number of lanes, geographic location in terms of latitude and longitude, pavement roughness (IRI), intersection, median, and ramp descriptors
  • No time-specific information, such as date, time, or weather is supplied.
  • No driver information is available.

3.1.6 Data Collection and Monitoring (DCM)

• National Transportation Communications for ITS Protocol (NTCIP) object definitions for Data Collection and Monitoring (DCM) embrace a range of roadside devices, including traditional traffic counters on the simple end, to scale-houses for weigh stations, in addition to other traffic data-gathering sensors. Due to the nature of these devices, no information along the lines of crash-related data is available from this system. The following are some characteristics of data elements available in NTCIP DCM:
  • Specifics relating to vehicle characteristics are available, such as number of axles, vehicle class, gross vehicle weight, clearance, height and width, and weight.
  • Information regarding traffic characteristics, such as headway and speed, is also provided in this data source.
  • Does not include any information relating to roadways or weigh stations, such as number of lanes, geographic location in terms of latitude and longitude, pavement roughness (IRI), intersection, median, and ramp descriptors.
  • No time-specific information, such as date, time, or weather is supplied.